Sudden cardiac arrest (SCA) is one of the leading causes of death in North America. But unlike other health problems of this magnitude, SCA is treatable. The treatment for most cases of SCA is immediate treatment with a defibrillator, a device that shocks the heart out of a fatal rhythm, allowing a normal, healthy rhythm to resume. Science and industry have developed an automated or semi-automated external defibrillator (collectively referred to as an “AED”) that provides a safe and effective treatment, and is automated enough to be used by non-medical personnel. AEDs can be placed at dispersed, non-hospital locations throughout a community to provide victims of SCA quick access to this treatment. For example, AEDs are now being placed in a wide range of settings such as clinics, offices and industrial locations, airports and airplanes, health clubs and golf courses.
An AED is a portable battery-operated device that analyzes a patient's heart rhythm, and, if appropriate, administers an electrical defibrillation shock (automated) or instructs an operator to administer the shock (semi-automated) to the patient via electrode pads. For example, such a defibrillator shock can often revive a patient who is experiencing ventricular fibrillation (VF).
AEDs typically require two levels of power to operate properly. An AED requires a high level of power generating a defibrillation shock, and a low level of power to operate circuitry, such as a microprocessor, while the AED is in use or during periodic—typically daily—self-testing while the AED is not in use. The high-power requirement is typically met using relatively expensive lithium batteries, which provide good power density (watts per cubic centimeter), the ability to deliver high-power pulses when needed, and a long shelf life. The low-power requirements can also be met from the lithium batteries. However, using the lithium batteries to power the microprocessor during self-testing may slowly discharge the batteries, thus shortening life and increasing field maintenance requirements by shortening the battery-replacement interval.